The present invention relates to a frequency combiner with a plurality of air-filled resonators connected to corresponding input ports. Each input port and corresponding resonator is connected to a common output port via a common resonator. The plurality of resonators are arranged such that they provide frequency selection and combining functions with a small dimension. The use of the common resonator mitigates phase differences of inter-resonator connections and minimizes insertion loss. The invention also relates to a frequency divider, whereby signals having different frequencies are provided to a common input port and common resonator. A plurality of resonating cavities, which resonate at different frequencies, are connected to the common resonator to separate signals of different frequencies to respective output ports.
In communications applications requiring transmission and/or reception over a plurality of closely-spaced frequency channels, it is preferable to combine the frequencies for transmission via a common antenna or other broadcast facility. This requires combining frequencies within the allotted bandwidth, while preventing interference between channels. Using a plurality of resonators permits sharing of a physical facility, such as an antenna, for broadcast. However, if multiple channels are served by the same facility, space constraints as well as cost constraints become important. For example, in a code-division multiple access (CDMA) system, two resonators are usually required per channel to achieve the required performance. The dual resonator configuration is commonly used for a 1-25 MHz bandwidth channel with a 2.5 MHz channel spacing. Larger bandwidth requirements require more resonators per channel. Known resonator arrays for combining multiple (N) channels for CDMA systems use an Nxc3x972 matrix. For instance, a known four-channel combiner uses a 4xc3x972 arrangement of resonators. This conventional resonator suffers from at least two deficiencies. First, the alignment of four resonators in a row provides a bulky arrangement that makes the combiner difficult to accommodate in a small space having width limitations. A dielectric resonator may be used to reduce the resonator size. However, use of the dielectric increases the cost of the frequency combiner and also introduces the mechanical complexity. Second, the conventional 4xc3x972 arrangement requires phase loop control to maintain a zero (or 180xc2x0) phase difference during inter-resonator transitions among CDMA channel signals. This complicates the design of the resonator matrix. The present invention obviates the above deficiencies by providing an Nxc3x97N matrix (Nxe2x89xa73), including a central common resonator cavity.
A multi-channel frequency multiplexer having combiner and divider functions is disclosed which minimizes phase difference, minimizes the size of the multiplexer and balances the insertion loss. As a combiner, the structure includes an Nxc3x97N matrix of frequency resonators, with a plurality of the resonators being provided with channel input ports. The resonators are interconnected with a common resonator, which in turn, is coupled to a common output port. The structure may also be used as a frequency divider having improved performance characteristics.